Magnetic hard disk drives are an example of information storage devices. Other information storage devices having some common or similar components or architecture include magneto-optical disk drives, optical disk drives, tape drives, and removable media disk drives.
Now referring to FIG. 1, a typical hard disk drive includes a head disk assembly (HDA) 10 and a printed circuit board assembly (PCBA—not shown in the view of FIG. 1) attached to a disk drive base 26 of a disk drive enclosure 16 of the HDA 10. The HDA 10 includes at least one disk 14a, 14b, and 14c, a spindle motor 30 for rotating the disks, and a head stack assembly (HSA) 32. The disks 14a, 14b, and 14c may be magnetic disks, magneto-optical disks, or optical disks, for example. The PCBA (not shown) includes electronics and firmware for controlling the rotation of the spindle motor 30 and for controlling the position of the HSA 32, and for providing a data transfer channel between the disk drive and its host.
The HSA 32 typically includes at least one head gimbal assembly (e.g. HGA 34). During operation of the disk drive, the HSA rotates to position the HGAs (e.g. HGA 34) adjacent desired information tracks on the surfaces 12a, 12b, 12c of the disks 14a, 14b, and 14c. Each HGA includes a head (to small to be visible in the view of FIG. 1) for reading and writing data from and to an adjacent disk surface (e.g. surfaces 12a, 12b, 12c). In magnetic recording applications, the head typically includes a slider and a magnetic transducer that comprises a writer and a read element. In optical recording applications, the head may include a minor and an objective lens for focusing laser light on to an adjacent disk surface. The slider is separated from the disk by a gas film that is typically referred to as an “air bearing.” The term “air bearing” is common because typically the gas is simply air. However, air bearing sliders have been designed for use in disk drive enclosures that contain other gases. For example, an inert gas like helium may be used because it does not degrade lubricants and protective carbon films as quickly as does oxygen. Helium may also be used, for example, because it has higher thermal conductivity than air, and therefore may improve disk drive cooling. Also, because the air bearing thickness depends on the gas viscosity and density, the air bearing thickness may be advantageously reduced in helium relative to air (all other conditions being the same). Furthermore, because helium has lower density than air, it may not buffet components within the disk drive as much, which may reduce track misregistration and thereby improve track following capability—facilitating higher data storage densities.
However, it may still be preferable for the disk drive to be air-filled during its operational lifetime. It is well known that disk drive enclosures that are designed to contain helium must be hermetically sealed to prevent an unacceptable rate of helium leakage, and such hermetic sealing may present additional design challenges and cost. For example, undesirable deflection of the top cover of the disk drive enclosure may occur with changes in barometric pressure in hermetically sealed disk drives. By contrast, such deflection may be mitigated in disk drives that contain air and so can include a breather filter (e.g. breather filter 20 having optional shroud feature 22) that allows atmospheric air to bleed into or out of the disk drive enclosure (e.g. disk drive enclosure 16 that includes base 26 and cover 28) through a breather hole (e.g. breather hole 18) to equilibrate the internal pressure within the disk drive with the external ambient air pressure.
In many air-filled disk drive designs, the fluid communication between the interior of the disk drive and the external environment (through the breather filter and breather hole) may also be required to pass through a narrow passage referred to as a “labyrinth” in order to limit the rate of flow and/or diffusion. The term “labyrinth” as used herein does not necessitate turns and bends; rather it refers to a narrow path that is longer than it is wide and restricts the rate of gas diffusion; it might have many turns and bends or it might be straight. The labyrinth may be part of the breather filter, like labyrinth 24 shown in FIG. 1, or alternatively may be fabricated as a groove or depression in the base 26 or cover 28.
One potentially advantageous trade-off that may be stricken between air-filled disk drive designs and helium-filled disk drive designs, is to (A) design the disk drive to operate as air-filled during its useful lifetime, for example so that it can employ a breather filter and breather hole, but (B) temporarily fill the disk drive with an alternative gas like helium during a particular portion of the disk drive manufacturing process (e.g. servo track writing) that may benefit most thereby (e.g. from a temporarily reduced flying height). However, accomplishing this advantageous trade-off requires a practical method to fill and replace the gas within the disk drive enclosure in a high-volume manufacturing environment. One proposed method requires removal of the disk drive top cover, while another requires leaving open a large hole in the disk drive top cover, so that the gas inside may be changed quickly in serial fashion. However, according to such proposed methods the disk drive is in a condition unsuitable for use outside of an artificially clean environment (e.g. a clean room or clean hood). Unfortunately, high-volume manufacturing operations that must be accomplished in clean rooms may be prohibitively burdensome and costly. Thus, there is a need in the art for a practical method to temporarily replace the gas in a disk drive enclosure, which may be suitable for high-volume manufacturing environments.